Why DEA if random tho? Maybe she was a rat?
The Secret Service, as people have mentioned, are prolly working on phone pings. I seem to recall the Secret Service being involved in the Jessica from Norton Shores disappearance from the get-go? For exactly that reason. I might be wrong on that.
But, yeah, the DEA and SONIC (South Oakland (County) Narcotics task force being involved strongly suggests LE has reason to suspect a drug nexus to this disappearance.
a couple speculative but perhaps plausible scenarios,
1. After leaving work early Friday, DS drove by her/a dealer's place to pick up something for the weekend; something happens there. dealer/whomever do whatever they did with DS and return her vehicle to her apt complex.
2. What the delivery guys I've seen in Chicago/Detroit do is they'll drive to you; but then either they come inside or have you jump in their ride with them and take a spin around the block to do the deal. Before either dropping you off down the block or back at your place.
What I've also seen and experienced, is that these deals are often not what you expect. The dealer will have extra people in the car with him. Maybe a couple girls. Maybe another customer. Maybe a cousin fresh out of prison. etc.
Or sometimes the dealer will dispatch one of his crew to make a delivery to you if he's in a different part of town and you're in a hurry. Again, same routine, dude pulls up, only this time it's some guy you've never seen before. You text the dealer, "WTH?" and the dealer says it's cool; it's his boy; go ahead and get in the car to make the deal.
I could see DS or anyone deciding to leave their purse behind in that scenario. Lock your valuables in your vehicle, take your keys and the cash needed and jump in.
DS, being in a hurry, might've texted the 420 delivery guy to meet her at her apt complex Friday after work. He gets there first. DS pulls up, parks in her spot and leaves her purse/wallet in her jeep. Takes her keys and the needed cash for the deal and gets in the delivery person's/people's vehicle.
Every dealer is always in a hurry once they get to you, for obvious reasons. So I could see DS not taking the time to drop off her purse / valuables inside her apt if the dealer's already there, waiting on her.